Ammunition



2 Sheets-Sheet 2 AMMUNITION c. D. cox

Filed June l2, 1940 June 9, 1942.`

E z Aanv ST55: As Denn/Al INVENTOR TeA-'Afef BY d/ ATToRNEYs CorpseALLOY 5755:

Ex reACr/au #were *t 'primers and/or powders unstable.

Patented June 9, 1942 AMMUNITION Charles D. Coxe, Bridgeport, Conn.,assignor to Remington Arms'Company, Inc., a corporation of DelawareApplication June 12, 1940, Serial No. 340,004 (c1. 14s- 12) 2 Claims.

This invention relates to the manufacture oi' ammunition components fromsteel and particularly from a steel that has a precipitation hardenablealloy therein. In the embodiment disclosed, the use of the steel isshown as applied to a cartridge case of the conventional rimflre.

type, but it lis to be distinctly understood that the invention may beapplied to any type of cartridge case andfor other ammunitioncomponents, such as for example, shotshell heads and center firecartridge primer cups.

Brass is in almost universal use as a cartridge ments in such use inregard to cost, shaping,

strength, corrosion resistance and extractibility after it `has beennreheated for four vhours at 450 C.

Fig. 5 is a graph showing the relation between Brinell hardness and timeof reheating of a copper alloy steel which has previously been nor-ymalized.

In Fig. 6 there appears a graph which shows the number of splits andextraction force required for various materials in various stages fromthe gun. Brass, however, has many dist advantages and much work andresearch have been expended in the search for a substitute which willstill meet the desired requirements.

Brass is expensive and cannot be used in combination with certain verydesirable primers and/or powders, as it will season crack, corrode, andwill also cause reactions renderingV the The matter of expenseV is ofparticular importance in the manufacture of the conventional rimrecartridges. There have been many attempts to use steel or' an alloythereof, but such has never proven feasible. The other` objects of theinvention will appear from the following description and illustrationswhich, as stated before,

'are not intended to limit the use of the invention to the forms shownand described.

In the drawings:

Fig. 1 is a sectional view of a rimiire cartridge case ywith the,clearance between the case and the chamber of the gun exaggerated, thebulging of the shell dueto 'firing pressures and a split beingalso'exaggerated.

Fig. 2 shows diagrammatically, by way of Fig. 4 is a graph showing therelation betweenv the relative elongation and the yield point andtensile strength of a copper bearing alloy which has been reduced insize by cold rolling. Two

- sets of curves appear in the graph, one for the metal as rolled afternormalizing and the second of treatment,l including the conventionalbrass -oase and a copper alloy lsteel treated in accord- Y ance with thepresent invention.

The purpose of a cartridge case is to be a container or carrier for thepowder and the priming mixture which initiates the `combustion of thepowder. The projectile is placed in the mouth of the cartridge case andis propelled from the barrel when the primer of the cartridge is struckby the firing pin, thereby igniting the propellent powder. When inposition in the gun, the s is located in the chamber thereof which isclosely matched with the size of the shell, the shell being properlysized in the course of manufacture so that it will fit into the chamber.It is obvious, however, that a certain clearance will always be presentbetween the outside of the case and the chamber. There is also avariation in the snugness'of the fit yoi! the case inthe' chamber andthe relative roughness of the chambers in different guns, all of whichaffect the operation of the cartridge and extraction thereof.

Referring to Fig. 1, lin which a conventional rlmflre shell is depicted,I0 represents the bolt .of the gun which has been closed against the 1head II of the case I2. 'I'he case I2 ts within the chamber I3 of thebarrel I 4 (shown fragmentarily); An extractor I5 of the conventionaltype engages the rim of the shell as it is pushed into the chamber I I.A suitable striker or firing pin 22 is provided to strike the rim of thecase I2 in which the priming mixture is placed. It is to be noted thatFig. 1 is a horizontal section and that the striker in the case of arimre shell contacts the case at or near the edge of the rim. It isnecessary that the material of the case have sufficient strength and asuillciently high yield point so that upon the combustion of the propellent charge and under the high pressure developed thereby, that itwill not be forced a subenough so that it will spring outwardly and sealthe chamber, and prevent the escape of gases from the chamber of thebarrel. In the event that the pressure is such as to cause the yieldpoint of the metal inthe shell to be exceeded thereby, allowing toogreat a permanent deformation to take place, it is obvious that thebulging portions of the shell will tightly engage the side of thechamber I3. This bulging of the shell will require an unusually highextraction force which in many instances causes the extractor I to pullthrough the rim or portion of the shell with which it engages as thebolt is moved backwardly, leaving the expended shell within the chamberand causing great inconvenience and dilcult operation. Even if theextractor does engage the shell and withdraw it, an excessive force isrequired to operate the gun, which obviously is undesirable. It is seen,therefore, that the yield point of the metal bears.` an importantrelationship to the extraction force necessary to withdraw the shell andalso to the sealing of the powder gases and prevention of the escapethereof through the mechanism of the gun and into the face of theoperator. Such leakage of gas. backwardly also detracts power from thepropelling of the projectile through the barrel of the gun and isundesirable. In the high velocity rimre cartridges of the present day;the powder pressures at the initial time of firing are in the vicinityof 18,000 pounds per square inch, and of the standard rimre shells inthelvicinity of 14,000 pounds per square inch. The ductility of themetal of the case must also be such that upon the firing thereof it willnot split, such as has been indicated at I1 of Fig. 1.

Brass shells also have the disadvantage of developing season cracks,which is attributed to the l dezincication of brass in the shell causedby eleparticular type of firearm, and it can also be seen 'that the testshowed no splits for the brass.

In Fig. 2, A, B, C. D, E, five of the steps in the forming of the usualrimre shell are shown, it

being understood that any number of intermedi# ate operations may beused or any type of shell or case may be formed similarly.

A is a cross section through a circular disc of metal. It is usual toboth form`the disc A from a strip of metal and at the same time pass itthrough a die byfmeans of a punch,A and cup it as shown in B of Fig. 2.vBy successive drawing operations, the shell and rimre case are shapeduntil they reach the iinal form shown in E.

In Fig. 3 is shown an enlarged view of a finished rimre shell in which,due to the drawing operations, the upper portion indicated at I8 hasbeen reduced by about 41% through the working. The section at I9 hasbeen reduced by about 35% and the section in the base 0%, or the baseremains substantially the same thickness asl the original. vlit isobvious that these amounts vary in accordance with the dies and processused and are not limited to those shown. It has been found by the heattreating process, hereinafter described, that an alloy steel containinga precipitation hardenable material may be made 'that will have theproper tensile strength and ductility to satisfactorily operate in agun, and tests have shown that it will have practically thesamefperformance characteristics as the brass, as 'far as extractionforce and splits are concerned, as can to make it impossible to usethem. It has also been diflicult to suitably draw and'form the cartridgecase from the strip of metal and still `have it so that it will functionin the chamber of a gun. By the use of a copper bearing alloy steel, ithas been found that it may be heat treated in the manner about tobedescribed, and ay successful cartridge case produced thereby.

In the heat treatment of ya steel, it is said to be normalized after 'ithas been brought to a temperature around or above 700 C., and thenallowed to cool in air. It might also be cooled by quenching to hastenthe cooling, or be allowed to remain in the furnace for a length oftime, either of which will result in a different grain structure of themetal than when it is cooled in air, depending upon the percent ofcarbon in the steel or other alloying elements. When copper or otheralloy making the steel precipitation hardenable, such as columbium,beryllium or titanium, is added to the steel, the steel may be heated tor100 C., preferably 800 to 900 C., at which time the copper goes intosolid solution in the iron; then,- upon cooling at a moderate rate suchas in air, the copper stays in the solid solution. These temperaturesare for copper as the precipitation hardenable element, and are-notnecessarily for the others. 'I'his may be termed solution heat treating.If then the articlebe subjected to a heat of between 400 and 616 C. andheld at that temperature for a period of from 16 hours to 10 minutes,respectively, as will be explained later, the copper which is in thesolid solution will tend to precipitate out of the solution, whether ornot this is complete not being known at present. However, it does have avery decided eiect upon the metal. The copper is thrown out of thesolution into a critically dispersed frm, which may or may not be aprecipitation, on reheating to a temperature that gives suiilicientatomic mobility to allow the change. There is a possibility thatsomerecrystallization will occur at the higher temperatures, but such isimmaterial. This last heat treatment is known as precipitationhardening. .The tensile and yield strengths of steels that have not beencold shaped before the precipitation .hardening are raised ysomewhat andthe ductility decreased slightly.- The graphs of Figs. 4 and 5,

representing work of Cyril S. Smith and Earl W. Palmer, are copyrightedby the American Institute of Mining and Metallurgical Engineers and areused with the permissionof that Institute. As may be seen by referringto Fig. 4, theyield point is raised from approximately 48,000 pounds persquare inch to 68,000 pounds per square inch in a copper alloy steel ofthe composition inditaken place.

cated when 0% reduction by cold rolling has The percentage elongation in2 inches, whichis an indication of the ductility, is seen to fall fromapproximately 28% to 24%. However, if cold shaping or working takesplace before the last heat treatment, such as occurs steel is increasedto 108,000 pounds per square inch, and that the ductility is reduced toabout 3%. Upon reheating the cold shaped'piece for 4 hours at 450 C., itis to, be noted that the yield point remains substantially the same, andyet the percentage elongation'is raised to about 121/2%.

This puts the formed steel case in condition such that it may besatisfactorily used in a lirearm because the yield strength has beenincreased to` such a point that permanent deformation will not takeplace-to any appreciable extent, 'thereby causing diiiicult extraction,nor will the shell split due to brittleness or lack oi' ductilitythereof. The period of time which it is necessaryA to reheat forprecipitation hardening the steel component depends upon the temperatureand probably the degree of work hardening. In Fig. 5 it may be seen thatif a temperature of 600 C. be used for a normalized copper alloy lsteelof the composition indicated, that the maxlmum Brinell hardness isreached in approxi-` mately 15 minutes, whereas if 450 C. be employedthe maximum Brinell hardness is reached at some time between 16 and 64hours, this Brinell hardness being slightly greater. l

It isl to be understood that the temperature used will depend upon thetime the component is subjected thereto and should be a timeternperature cycle wherein no or little recrystallization takes place.It has been found that a shell may be placed into a heat treatingfurnace and, when the shell reaches 616 C. in a period of 10 minutes,that satisfactory results will be obtained. If 'higher temperatures areused, a much shorter time of treatment must be employed or substantialrecrystallization will take place, and the results will not besatisfactory.

Referring to Fig. 3, it is seen' that in a conlventional rimiirecartridge there is a much larger reduction of the wall near the mouththan there is near the lower part, and that in the base there issubstantially no reduction. In the exand characteristics is combinedwith a base having the desired properties.

During the cold shaping process of a rimre shell, such as shown in Fig.3, considerable strain is set up at the bend portion of the rim, which Iserves to work harden to a slight extent in this particular area. Theheat treating temperature serves to relieve the stresses at this point,vwhich also assists the sensitivity characteristics of the shell becausethe priming mixture is contained in the rim.

Referring now to Fig. 6, various types of shells have been tested and acomparison indicated. For brass, extraction force was found to be in theneighborhood of 5 pounds and no splits were recorded. The copper alloysteel after normalizing and drawing gave about splits and 5 poundsextraction force. The same copper alloy steel upon the precipitationhardening treatment gave 0% splits and 5 pounds extraction force, whichis substantially identical tothe brass. It is preferable to use an alloysteel that has carbon in a low amount, not over .50% and preferablyv.10% or under. In order to strengthen or give desirable properties tothe steel, any'of the following elements singly or in lcombination inthe amounts indicated may be used.

Molybdenumnot over 1.00%, preferably less than 0.50%

Chromium-not over 5.00%, preferably 0% to 2.00% Vanadium-0% to 1.00%,

or other ,alloying elements in such proportion ample shown, this is 41%near the mouth, 35%l at the lower part of the wall, and 0% Vat the base.-By referring to Fig. 4, it is noted that -when the blank or cup issubjected, first, to a normalizing treatment, then is cold shaped, and

then is reheated for. the purpose of precipitation hardening, that atthe mouth, the copper alloy steel as indicated in Fig. 4 will have ayield strength in the vicinity of 108,000 pounds i per square inch andthat the elongation will be suilicient strength and ductility producedby the cold working and precipitation hardening to withstand the firingpressures. It is also to be noted that the base is suiiiciently soft sothat the impact of the firing pin will be properly transmitted to theprimer mixture, the strength rt this point beingimmaterial because it isbacked up by the bolt and does not receive the same forces that the casedoes near the mouth and along the wall. The advantage of such adistribution of strength and ductility in a cartridge case is obviousfrom the foregoing in that a shell with a wall that is of the properstrength as will increase the strength of the steel without so loweringthe ductility as to make it impossible to fabricate.` The phosphorusshould be not over .50% and preferably under .25%. The copper in thesteel should behot over 5.00% and preferably under 3.00%. As an example,the

following steels have been found to besatisfactory: l .'No. 1

Per cent Carbon. .08

Manganese .50

' Silicon .l0

Nickel 2.00

Phosphorus maximum-- .04

Sulphur do .04

Copper l 00 Per cent Carbon .08

Manganese .40

Nickel 1.00

.Copper 1.30

y Molybdenum .20

Phosphorus maximum .04

Sulphur do .04

It is to be understood, however, that the invention is not limited tothese two alloys, but

that they are cited merely as examples of some stantially 50,000 poundsper squareinch or more in the normalized steel and which renders thetionI of the copper from solid solution.

splits.

steel capable of being precipitation hardened falls within the scope ofthe invention, the precipitation hardening serving to keep the yieldstrength of the cold shaped sections substantially constant and toincrease the ductility so that the shell will function satisfactorily.It has been found that the best results are obtained with an alloy steelin which the copper is in excess of 0.5% and preferably between 1 and2%. The shell is heated at some point, C or before of Fig. 2, to about700 C. and preferably 800 to 900 C., and is maintained at thistemperature for a suiiicient time to rmit the copper to go into solidsolution in t e iron. The component is then allowed to cool at amoderate rate,

v such as in air or room temperature, this being fast enough to preventany substantial precipita- The ishell is then worked into a form suchias in D of Fig. 2 so that the material of the walls of the shellreceive cold working such as shown in Fig. 3, causing work hardening ofthe portions indicated. The shell in this condition, due to the increasein yield point, will probably have a low extraction force, as shown inFig. 6 but, due tothe lackof ductility, a large percentage of splitswill take place. At this ypoint or at D the shell Vis subjected to atemperature preferably between 400 and 616 C. and held there frombetween 16 hours to 10 minutes as indicated generally by Fig. 5, andpreferably 450 to 500 C. for 4 hours. This gives the required ductilitywith only a slight change in theA yield point or elastic limit, becausethe simultfaneous precipitation hardening due to copper content willcompensate forthe loss in yield strength which ordinarily accompaniesthe heating of cold worked steel. It is to be noted that' the graph ofFig. 5 is for illustrative .purposes only and' does not necessarilyrepresent the preferred metal to be used. As a specific example, eithersteel' I or 2, composition of which is set forth above, after step B,Fig. 2, is annealed at 620 C. to facilitate the drawing operation ofstep C of Fig. 2. After step C, the shell is heated at 870 C. for 1/2hour and then air cooled.l After step E, Fig. 2,l the shell is heatedto450 C. for 4 hours and will then give the results substantially as shownin Fig. 6 in which the extraction force will be around 5 pounds andthere will be no thereon.

It is to be understood that the annealing step is not essential nor isthe normalizing or solutionl heat treating at 870 C., providing thesteel can be properly drawn without cracking or undue wear and strainofthe dies, and the normalizing is not necessary if, in the manufactureof the shell from which the component is cut, the sheet was so.processed as to place the copper in solid solution in the iron.

YIf desired, the steel may be plated with copper or other rustinhibiting material placed It is evident from the foregoing descriptionthat a method has been evolved and a novel ammunition component producedthat is superior in many `ways to those in present day use. As

l. In the manufacture of a cartridge shell, themethod which comprisesproviding a disc of low carbon steel containing a precipitationhardenable element; cold shaping said disc into a head of substantiallythe thickness of said disc and a Ybody integral with said head whichdecreases in wall thicknesstoward the open end thereof;

andc precipitation hardening the shell thus formed, whereby issecured amaximum ductility in saidrhead and an increasing yield strength towardthe mouth of said body. v

2. In' the manufacture of rimre cartridge shells, the method whichcomprises providing a disc of low carbon steel containing copper in astate of solid solution, cold working said disc to form therefrom acartridge shell 'comprising a head of substantially the thickness ofsaid disc and a body of lesser thickness joined to said headby anintegral folded hollow rim, and subsequently precipitation hardening theshell thus formed to increase the ductility of the metal v withoutmaterial decrease in the yield strength the scope of the appended

